The capacitor main body of a multilayer ceramic capacitor includes ceramic dielectric layers and internal electrode layers alternately stacked. External electrodes are formed on end faces, where the internal electrode layers are exposed, of the capacitor main body. In recent years, reducing the thickness of and increasing the number of ceramic dielectric layers and internal electrodes to be stacked has been pursued to satisfy the demand for size-reduction and higher capacitance.
Such ceramic dielectric layers configuring a multilayer ceramic capacitor, for example, include dielectric materials mainly containing barium titanate powders. If the internal electrode layers include base metal such as Ni, they are sintered usually in nitrogen-hydrogen atmosphere in which the ceramic dielectric layers are reduced to become semiconductor. That is a problem.
In order to overcome this problem, for example, proposed is a dielectric material having a larger ratio of barium site to titanium site of barium tatanate powders than that of stoichiometric ratio (see patent document 1). Also, proposed is a dielectric material containing barium titanate powders and additives such as manganese oxide (MnO), rare earth oxide and magnesium oxide (MgO) (see patent document 2).
These proposed materials have durability against reduction and show high relative dielectric constant. Therefore, such materials have been preferably used for multilayer ceramic capacitors having thickness of 10 micrometer or more among capacitors which has already been manufactured. However, in multilayer ceramic capacitors having 5 micrometers or less as a result of reducing thickness in recent years, above-mentioned dielectric materials easily obtain grain growth, thereby reducing in number of grains disposed in one ceramic dielectric layer. Consequently, the insulating property is low and reliability in a highly accelerated life test involving application of DC voltage at high temperature is low.
More recently, a new dielectric material having high relative dielectric constant and high insulating property at a thickness of 5 μm or less (see patent document 3). The dielectric material disclosed in patent document 3 includes barium titanate powder (hereinafter, it is called BT powder) as a main component, and 0.02 wt % of alkali metal oxide as an impurity therein. The material also includes 2 or more rare earth oxides having different ion radii with at least one selected from scandium oxide and yttrium oxide, and at least one from gadolinium oxide, terbium oxide and dysprosium oxide.    Patent Document 1: Japanese Examined Patent Application No. 57-42588    Patent Document 2: Japanese Patent Application Laid-Open No. 61-101459    Patent Document 3: Japanese Patent Application Laid-Open No. 10-223471